Methods developed in the principal investigator's laboratory have been used to select for mutants of the Mitochondrial respiratory chain. Many of these mutants exhibit a new pathway of respiration that is insensitive to cyanide or antimycin A. It is proposed to study the cyanide-insensitive pathway in order to determine the nature of the polypeptide(s) involved, the location f the genes coding for them, and the mechanism of oxygen reduction. Previous experiments have shown that a mitochondrial gene product is involved in the regulation of the cyanide-insensitive pathway and experiments with mutants and heterocaryons will be carried out to determine the exact nature of this regulatory process. In addition, experiments wll be carried out to determine the regulation of the mitochondrially synthesized polypeptides associated with cyto hrome oxidase.